The present patent application refers to an hydraulic valve controlled by a photoelectric cell and operated by an electric motor.
The valve according to the present invention has been specifically designed for installation in hydraulic systems in which the delivery of water is controlled by a photoelectric cell that is excited when the user's hands or body approach the fitting used to deliver the water, such as faucets, water closets, public urinals.
The use of these automatically operated hygienic-sanitary fittings is getting more and more popular in the bathrooms of public places, such as bars, restaurants or service areas on highways.
The solenoid valves that are normally used in these hydraulic systems controlled by a photoelectric cell generally consist in an electromagnet that is excited and remains excited as long as the user stays near the hygienic-sanitary fitting, so that the water is delivered in a fully automatic way and only for a limited time interval.
Due to the high power absorption, however, this type of solenoid valves is not suitable for situations in which batteries are used in absence of the supply mains or when no outlet is available next to the hydraulic system concerned.
Under these circumstances, the hydraulic systems use special low-energy consumption solenoid valves that are excited by a photoelectric cell just for the few seconds necessary to open or close them.
These special solenoid valves are basically composed of a bistable electromagnet, whose slug is subject to the opposed action of a return spring and of a permanent magnet, that cause the slug to maintain its stop position, once the excitation of the coil has ended.
In order to reduce the power absorption, these solenoid valves feature very low values of slug stroke and therefore the slug is subject to the attractive action of the permanent magnet even while it is retained by the return spring. Moreover, the dimensions of the return spring must allow for very narrow tolerances in order for the return force to be balanced by the opposed force of the permanent magnet.
It is easily understood how critical this operating system is, since it is based on a highly unstable balance of forces that tend to draw the slug towards two opposite stop directions, in correspondence with the opening and the closing of the valve.
This means that in this type of bistable electromagnets, the opening or closing of the valve can take place for accidental reasons, regardless of the command signal sent by the photoelectric cell, such as water hammering in the water supply, impurities contained in the water, time variation of the opposed forces of the permanent magnet and of the return spring.
Apart from the above-mentioned unreliability, the said bistable electromagnets have the disadvantage of being affected by the water supply pressure, due to the operating principle of the slug, that is the higher the water supply pressure, the higher the necessary force and therefore the power absorbed by the electromagnet to move the slug.